U.S. patent number 8,064,985 [Application Number 10/660,825] was granted by the patent office on 2011-11-22 for system and method for determining the position of a flexible instrument used in a tracking system.
This patent grant is currently assigned to GE Medical Systems Global Technology Company. Invention is credited to Thomas Herbert Peterson.
United States Patent |
8,064,985 |
Peterson |
November 22, 2011 |
System and method for determining the position of a flexible
instrument used in a tracking system
Abstract
A medical instrument for use in an image guided surgery system,
including a support member operatively connected to a flexible
engaging member, and a strain gauge affixed to a portion of the
flexible engaging member. The strain gauge is configured to detect
deflection of the flexible engaging member.
Inventors: |
Peterson; Thomas Herbert
(Wilmington, MA) |
Assignee: |
GE Medical Systems Global
Technology Company (Waukesha, WI)
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Family
ID: |
34218156 |
Appl.
No.: |
10/660,825 |
Filed: |
September 12, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050059883 A1 |
Mar 17, 2005 |
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Current U.S.
Class: |
600/424;
606/130 |
Current CPC
Class: |
A61B
34/20 (20160201); A61B 90/00 (20160201); A61B
17/34 (20130101); A61B 90/06 (20160201); A61B
2090/064 (20160201); A61B 2034/2051 (20160201); A61B
2034/2068 (20160201); A61B 2017/00292 (20130101); A61B
17/06 (20130101); A61B 2090/067 (20160201); A61B
2034/2072 (20160201) |
Current International
Class: |
A61B
19/00 (20060101) |
Field of
Search: |
;600/424
;73/862.451 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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63241409 |
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Oct 1988 |
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JP |
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2002095630 |
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Apr 2002 |
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JP |
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WO 02/36018 |
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May 2002 |
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WO |
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Other References
Davidson, Tish. "Pulmonary artery catheterization". Encyclopedia of
Medicine 20010406. FindArticles.com Dec. 12, 2007.
http://findarticles.com/p/articles/mi.sub.--g2601/is.sub.--0011/ai.sub.---
2601001143. cited by examiner .
Tanaka et al. Needle Deflection and Sewability on Lockstitch Sewing
Machine. Journal of the Textile Machinery Society of Japan. vol.
43(3) p. 71-78. 1997. cited by examiner.
|
Primary Examiner: Casler; Brian
Assistant Examiner: Mehta; Parikha S
Attorney, Agent or Firm: McAndrews, Held & Malloy, Ltd.
Baxter; William
Claims
The invention claimed is:
1. A medical instrument for use in an image guided surgery system,
comprising: a medical instrument comprising: a support member
operatively connected to a flexible engaging member having an
operative distal tip; upper and lower strain gauges affixed to an
outer portion of said flexible engaging member, wherein said upper
and lower strain gauges are configured to detect movement of said
operative distal tip of said flexible engaging member and generate
deflection data signals; a tracking system configured to track said
medical instrument; a control system configured to correlate said
deflection data signals from said upper and lower strain gauges
with amounts of deflection of the flexible engaging member and
further configured to combine tracking information from the
tracking system with the deflection data; and a display configured
to display a position of the medical instrument including the
position of the flexible engaging member over previously obtained
images of a patient.
2. The medical instrument of claim 1, wherein a resistance of said
strain gauge changes when said flexible engaging member
deflects.
3. The medical instrument of claim 2, wherein said strain gauge is
within an electrical circuit in which a potential difference occurs
when said resistance of said strain gauge changes.
4. The medical instrument of claim 1, wherein said flexible
engaging member is one of a needle, catheter, curette, and K
wire.
5. The medical instrument of claim 1, further comprising at least
one additional strain gauge affixed to said flexible engaging
member.
6. The medical instrument of claim 1, wherein said portion of said
flexible engaging member is proximate to said support member.
7. The medical instrument of claim 1, wherein said strain gauge
provides information regarding a location of said operative distal
tip in relation to a longitudinal axis of said support member.
8. An image guided surgery system, comprising: a medical instrument
having a flexible engaging member operatively connected to a
support member, said flexible engaging member having a deflectable
operative distal tip at least one of an electromagnetic, optical,
inertial position, and ultrasound tracking system configured to
track said medical instrument; and a deflection tracking system
configured to track said flexible engaging member of said medical
instrument, said deflection tracking system comprising at least one
strain gauge affixed to an outer portion of said flexible engaging
member in order to detect movement of said deflectable operative
distal tip.
9. The image guided surgery system of claim 8, wherein a resistance
of said at least one strain gauge changes when said flexible
engaging member moves.
10. The image guided surgery system of claim 9, wherein said at
least one strain gauge is within an electrical circuit in which a
potential difference occurs when said resistance of said strain
gauge changes.
11. The image guided surgery system of claim 10, further comprising
a processing unit that correlates said potential difference with an
amount of movement of said flexible engaging member.
12. The image guided surgery system of claim 8, further comprising
a display for showing a position of said medical instrument within
an operating area of a patient.
13. The image guided surgery system of claim 8, wherein said
flexible engaging member is one of a needle, catheter, curette, and
K wire.
14. The medical instrument of claim 8, wherein said portion of said
flexible engaging member is proximate to said support member.
15. The image guide surgery system of claim 8, wherein said at
least one strain gauge provides information regarding a location of
said deflectable operative distal tip.
16. A method of navigating a medical instrument having a flexible
engaging member having an operative distal tip, the method
comprising: tracking the medical instrument with a first position
tracking method that tracks a proximal end of the medical
instrument; and using a second tracking method to track movement of
the operative distal tip of the medical instrument, wherein said
using comprises affixing a strain gauge on an outer portion of the
operative distal tip of the medical instrument in order to detect
movement of the operative distal tip.
17. The method of claim 16, comprising measuring a change in
voltage that arises from a change in resistance of the strain gauge
upon deflection of the operative distal tip.
18. The method of claim 17, wherein said affixing comprises
affixing the strain gauge on the portion of the flexible engaging
member that is proximate a support member of the medical
instrument.
19. The method of claim 17, wherein said affixing comprises
affixing at least one other strain gauge on the outer portion of
the flexible member of the medical instrument.
20. The method of claim 17, further comprising correlating the
change in voltage to an amount of deflection of the flexible
engaging member.
21. The method of claim 16, further comprising combining data
received from said tracking and using and displaying a position of
the medical instrument based on the combined data.
22. The method of claim 16, wherein said first tracking method
comprises one of an electromagnetic, optical, inertial position and
ultrasound tracking method.
23. The method of claim 16, wherein said affixing the strain gauge
on the outer portion of the operative distal tip of the medical
instrument in order to detect movement of the operative distal tip
provides information regarding a location of the operative distal
tip.
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to flexible instruments,
such as needles, probes, catheters, curettes and the like, used in
image guided applications, such as image guided surgery. In
particular, the present invention relates to a system and method
for determining the position of a flexible instrument during an
image guided application.
Many medical procedures involve a medical instrument, such as a
drill, a catheter, scalpel, scope, stent or other tool. In some
cases, a medical imaging or video system may be used to provide
positioning information for the instrument, as well as
visualization of an interior of a patient. However, medical
practitioners often do not have the use of medical imaging systems
when performing medical procedures. Typically, medical imaging
systems are too slow to produce useable real-time images for
instrument tracking in medical procedures. The use of medical
imaging systems for instrument tracking may also be limited for
health and safety reasons (e.g., radiation dosage concerns),
financial limitations, physical space restrictions, and other
concerns, for example.
Medical practitioners, such as doctors, surgeons, and other medical
professionals, often rely upon technology when performing a medical
procedure, such as image-guided surgery or examination. A tracking
system may provide positioning information of the medical
instrument with respect to the patient or a reference coordinate
system, for example. A medical practitioner may refer to the
tracking system to ascertain the position of the medical instrument
when the instrument is not within the practitioner's line of sight.
A tracking system may also aid in presurgical planning.
The tracking or navigation system allows the medical practitioner
to visualize the patient's anatomy and track the position and
orientation of the instrument. The medical practitioner may use the
tracking system to determine when the instrument is positioned in a
desired location. The medical practitioner may locate and operate
on a desired or injured area while avoiding other structures.
Increased precision in locating medical instruments within a
patient may provide for a less invasive medical procedure by
facilitating improved control over smaller instruments having less
impact on the patient. Improved control and precision with smaller,
more refined instruments may also reduce risks associated with more
invasive procedures such as open surgery.
Tracking systems may be ultrasound, inertial position, optical or
electromagnetic tracking systems, for example. U.S. Pat. No.
5,803,089, entitled "Position Tracking and Imaging System for Use
in Medical Applications," issued to Ferre, et al. (the "'089
patent"), and U.S. Pat. No. 6,484,049, entitled "Fluoroscopic
Tracking and Visualization System," issued to Seeley, et al. (the
"'049 patent") both describe surgical tracking and navigation
systems. The '089 patent and the '049 patent are hereby
incorporated by reference in their entireties. Tracking systems
using optical detection (video camera and/or CCDs (Charge Coupled
Devices)) have been proposed for monitoring the position of a
medical instrument with respect to a reference unit as mentioned in
U.S. Pat. No. 5,230,623, entitled "Operating Pointer with
Interactive Computergraphics," issued to Guthrie, et al. (the "'623
patent"). Further, tracking systems using ultrasonic detection are
also disclosed in the '623 patent
Electromagnetic tracking systems may employ coils as receivers and
transmitters. Typically, an electromagnetic tracking system is
configured in an industry-standard coil architecture (ISCA). ISCA
uses three colocated orthogonal quasi-dipole transmitter coils and
three colocated quasi-dipole receiver coils. Other systems may use
three large, non-dipole, non-colocated transmitter coils with three
colocated quasi-dipole receiver coils. Another tracking system
architecture uses an array of six or more transmitter coils spread
out in space and one or more quasi-dipole receiver coils.
Alternatively, a single quasi-dipole transmitter coil may be used
with an array of six or more receivers spread out in space.
The ISCA tracker architecture uses a three-axis dipole coil
transmitter and a three-axis dipole coil receiver. Each three-axis
transmitter or receiver is built so that the three coils exhibit
the same effective area, are oriented orthogonally to one another,
and are centered at the same point. If the coils are small enough
compared to a distance between the transmitter and receiver, then
the coil may exhibit dipole behavior. Magnetic fields generated by
the trio of transmitter coils may be detected by the trio of
receiver coils. Using three approximately concentrically positioned
transmitter coils and three approximately concentrically positioned
receiver coils, for example, nine parameter measurements may be
obtained. From the nine parameter measurements and a known position
or orientation parameter, a position and orientation calculation
may determine position and orientation information for each of the
transmitter coils with respect to the receiver coil trio with three
degrees of freedom.
Typically, conventional tracking system such as those discussed
above, are used to track rigid medical instruments, such as
aspirating devices, surgical drills, cutting instruments and the
like. However, various surgical applications use flexible
instruments such as curettes, needles, catheters, endoscopes, wires
and the like that may deflect while navigated within an operating
space of a patient. The conventional tracking systems usually are
not capable of tracking the deflecting tips of these flexible
instruments. Rather, these systems typically accurately track only
a proximal end of the instrument that does not deflect. Hence, the
systems may display a position of the medical instrument that is
not accurate. A surgeon or physician may move the instrument based
on the inaccurate information and damage internal structures of the
patient.
Thus, a need exists for a system and method that accurately tracks
the position of a medical instrument, including a distal operative
end of the medical instrument.
SUMMARY OF THE INVENTION
Certain embodiments of the present invention provide a medical
instrument for use in an image guided surgery system. The medical
instrument includes a support member operatively connected to a
flexible engaging member, and a strain gauge affixed to a portion
of the flexible engaging member. The strain gauge is configured to
detect deflection of the flexible engaging member. The measured
resistance of the strain gauge changes when the flexible engaging
member deflects. The strain gauge is a resistor within an
electrical circuit, such as a Wheatstone bridge, in which a
potential difference occurs when the resistance of the strain gauge
changes. The medical instrument may be used in an image guided
surgery system that includes a tracking system that is separate and
distinct from a deflection tracking system that includes the strain
gauge(s). The additional tracking system may be an electromagnetic,
optical, inertial position, or ultrasound tracking system
configured to track the medical instrument.
The flexible engaging member may be a needle, catheter, curette,
endoscope, or K wire. The medical instrument may include at least
one additional strain gauge affixed to the flexible engaging
member. The strain gauge(s) is affixed to a portion of the flexible
engaging member that is proximate to the support member.
Certain embodiments of the present invention also provide a method
of navigating a medical instrument having a flexible engaging
member used in image guided surgery. The method includes tracking
the medical instrument with a first position tracking method that
tracks a proximal end of the medical instrument; and using a second
tracking method to track deflections of an operative member of the
medical instrument located at a distal end of the medical
instrument. The method also includes combining data received and
displaying a position of the medical instrument based on the
combined data.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 illustrates a medical instrument according to an embodiment
of the present invention.
FIG. 2 illustrates a simplified diagram of a strain gauge according
to an embodiment of the present invention.
FIG. 3 illustrates a top view of a strain gauge according to an
embodiment of the present invention.
FIG. 4 is a circuit diagram of a Wheatstone bridge according to an
embodiment of the present invention.
FIG. 5 illustrates a cross-sectional axial view of a flexible
engaging member according to an alternative embodiment of the
present invention.
FIG. 6 illustrates an electromagnetic tracking system according to
an embodiment of the present invention.
FIG. 7 illustrates a flow chart of a method of accurately tracking
a position of a medical instrument during image guided surgery.
The foregoing summary, as well as the following detailed
description of certain embodiments of the present invention, will
be better understood when read in conjunction with the appended
drawings. For the purpose of illustrating the invention, there is
shown in the drawings, certain embodiments. It should be
understood, however, that the present invention is not limited to
the arrangements and instrumentalities shown in the attached
drawings.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a medical instrument 10 according to an
embodiment of the present invention. The medical instrument 10
includes a rigid support member 12, such as a handle, a main body
housing electronics and the like, or mounting assembly, and a
flexible tip or engaging member 14. The flexible engaging member 14
includes a proximal end 15 (near the support member) and a distal
operative end 17. The flexible engaging member 14 is the operative
end of the medical instrument 10. The flexible engaging member may
be a flexible probe, needle, curette, K wire, catheter or various
other such devices that are susceptible to deflection, flexing, and
other such movements.
Strain gauges 16 and 18 are positioned on the flexible engaging
member 14 proximate a distal end 20 of the support member 12. The
strain gauges 16 and 18 are configured to detect deflection in the
flexible engaging member 14, as discussed below. The strain gauges
16 and 18 may be positioned on any portion of the flexible engaging
member 14. However, the strain gauges 16 and 18 are preferably
positioned on a portion of the flexible engaging member 14 that
substantially bends, or deflects, when a force is applied to the
flexible engaging member 14. For example, the strain gauges 16 and
18 may be positioned proximate the support member 12 of the medical
instrument.
FIG. 2 illustrates a simplified diagram of a strain gauge system 22
according to an embodiment of the present invention. The system 22
includes a rigid support 24, a flexible member 26 extending
perpendicularly from the rigid support 24, and an upper strain
gauge 28 and a lower strain gauge 30 affixed to the flexible member
26. The rigid support 24 is analogous to the distal end of the
support member 12, while the flexible member 26 is analogous to the
flexible engaging member 14 shown in FIG. 1.
FIG. 3 illustrates a top view of a strain gauge 28 or 30. Each
strain gauge 28 and 30 includes a piece of wire 32 bonded to a
flexible plastic backing 34. Connecting leads 36 electrically
connect the ends 38, 40 of the wire to other elements within an
electrical circuit (not shown).
Referring again to FIG. 2, when a force is applied to the flexible
member 26 in the direction of F, thereby moving the flexible member
26 in an arcuate path about a pivot point 27 in the direction of
F', the length of the upper strain gauge 28 increases and its
cross-sectional area decreases. As the length of the upper strain
gauge 28 increases and its cross-sectional decreases, the
resistance of the upper strain gauge 28 increases, as shown by
equation (1): R=.rho.L/A (1) where R=resistance, L=length of the
strain gauge, A=cross sectional area of the strain gauge, and
.rho.=resistivity of the strain gauge.
Further, when the flexible member 26 is moved in the direction of
F', the length of the lower strain gauge 30 decreases, and its
cross-sectional area increases, thereby causing the resistance of
the lower strain gauge 30 to decrease. The changes in resistance
may be detected by a Wheatstone bridge circuit as shown in FIG.
4.
FIG. 4 is a circuit diagram of a Wheatstone bridge 42 according to
an embodiment of the present invention. The Wheatstone bridge 42
includes resistors R.sub.1 and R.sub.2, strain gauges 28 and 30
(shown as resistors), and a source of electromotive force (emf) 44.
The strain gauges 28 and 30 are used within the Wheatstone bridge
42. Resistors R.sub.1 and R.sub.2 are selected such that the
Wheatstone bridge 42 is balanced when no force is applied to the
flexible member 26 of the strain gauge system 22 shown in FIG. 2.
When the Wheatstone bridge 42 is balanced, there is no potential
difference between the points a and b. However, when a force is
applied to the flexible member 26, the resistance of each strain
gauge 28 and 30 changes and the Wheatstone bridge 42 is no longer
balanced. Consequently, a potential difference appears between
points a and b that is proportional to the magnitude of the force
applied to the flexible member 26.
Referring again to FIG. 2, the strain gauge system 22 is configured
to output a change in resistance that is directly proportional to
the amount of force applied in the direction of F. For example, if
a force of magnitude F.sub.1 is applied to the flexible member 26,
a potential difference appears between points a and b of the
Wheatstone bridge. Further, the flexible member will move a
particular distance over path F' as a result of the force F.sub.1
applied. Thus, a potential difference V.sub.1 is directly
proportional to a distance of deflection over the path F'. A direct
linear relationship exists between the amount of deflection and the
potential difference. The distance the flexible member deflects
yields a unique potential difference V.sub.EX. Consequently,
various potential differences output from a circuit having the
strain gauges 28 and 30 allow one to know the amount the flexible
member 26 deflects. Equation (2) shows the relationship between
strain/compression and potential difference:
V.sub.S/V.sub.G=(G(e))/2 (2) where V.sub.S=voltage supplied,
V.sub.G32 potential difference due to strain/compression, G=a gauge
factor, and e=the amount of strain/compression. The
strain/compression of a strain gauge, such as strain gauges 28 and
30, yields a potential difference V.sub.G. The potential difference
may be correlated to the strain/compression. That is, a measurement
of potential difference allows one to determine the amount of
strain/compression of the strain gauges 28 and 30. Further, an
amount of strain/compression allows one to know the amount the
flexible member 26 deflects. Each measured potential difference
allows one to determine the amount of strain/compression on the
strain gauge 28 or 30, which in turn provides information regarding
the amount of deflection of the flexible member 26. Thus, each
particular potential difference may be correlated to an amount of
deflection of the flexible member 26. A measurement of the
potential difference V.sub.G allows one to calculate an amount of
deflection of the flexible member 26.
Turning again to FIG. 1, the principles described above may be
applied to the medical instrument 10. The strain gauges 16 and 18
are affixed above and below the flexible engaging member 14. Thus,
as the flexible engaging member 14 is deflected, the strain gauges
16 and 18 strain or compress. As the strain gauges 16 and 18 strain
or compress, the lengths and cross-sectional areas of the strain
gauges change, as described above. For example, as a strain gauge
16 or 18 strains, its length increases and its cross-sectional area
decreases, thereby increasing its resistance. Further, if a strain
gauge 16 or 18 compresses, its length decreases and its
cross-sectional area increases, thereby decreasing its resistance.
Because the strain gauges are included within a Wheatstone bridge
circuit 42, as shown in FIG. 4, a potential difference arises
within the Wheatstone bridge circuit that is proportional to the
distance of deflection of the flexible engaging member 14. Each
measured potential difference corresponds directly to an amount of
deflection of the flexible engaging member 14.
FIG. 5 illustrates a cross-sectional axial view of the flexible
engaging member 14 according to an embodiment of the present
invention. The flexible engaging member 14 includes the upper
strain gauge 16 and the lower strain gauge 18. The flexible member
14 may also have lateral strain gauges 46 affixed thereto for
providing additional information regarding lateral deflection of
the flexible engaging member 14. Optionally, the strain gauges 16,
18, and 46 may be solid state strain gauges.
FIG. 6 illustrates an electromagnetic tracking system 100 according
to an embodiment of the present invention. The system 100 includes
a headset 112 mounted on a patient 114, the medical instrument 10,
a control system 118, and a display 120. The control system 118,
which is in electrical communication with the medical instrument
10, the headset 112 and the display 120, includes a position
detection unit 122, a registration unit 124, and an image storage
unit 126. The image storage unit 126 stores sets of prerecorded
images such as CAT, MRI, or PET scan images. Each set of images may
be taken along, for example, coronal, sagittal or axial
directions.
The system 100 also includes a receiver assembly, including
magnetic sensors, positioned on the headset 112. The receiver
assembly is configured to detect a magnetic field. A transmitter
assembly is positioned on the medical instrument 116. The
transmitter assembly is configured to generate a magnetic field
that is detected by the receiver assembly. Alternatively, the
receiver assembly may be positioned on the medical instrument 16,
while the transmitter assembly may be positioned on the headset 12.
Optionally, the medical instrument 10 may be used with various
other tracking systems, such as ultrasound, inertial position and
optical tracking systems.
The system 100 operates to track the medical instrument 10 with
respect to the headset 12 through various methods known in the art.
The control system 118 tracks the medical instrument through
electromagnetic tracking and through the strain gauges 16 and 18.
As the medical instrument 10 is inserted into the patient 14, the
flexible engaging member 14 may deflect, as described above, as it
encounters anatomical structures within the patient 14.
The general position of the medical instrument 10 may be tracked
through electromagnetic tracking. That is, an electromagnetic
tracking system may accurately track the proximal end 15, i.e., the
end closest to the support member 12, of the flexible engaging
member 14. The deflection of the distal end 17 of the flexible
engaging member 14 is detected by a deflection tracking system that
includes the strain gauges 16 and 18. The strain gauges 16 and 18,
which are in electrical communication with the control system 118,
relay deflection data signals to the control system 118. The
control system 118 then processes both the information received
from the electromagnetic tracking members (i.e., the receiver
assembly and the transmitter assembly) and the strain gauges 16 and
18. The control system 118 correlates received data from the strain
gauges with amounts of deflection of the flexible engaging member
14. The control system 118 then combines the electromagnetic
tracking information with the deflection data and displays a
position of the medical instrument 10, including the position of
the flexible engaging member 14, on the display 120 over previously
obtained images of the patient.
FIG. 7 illustrates a flow chart of a method of accurately tracking
a position of the medical instrument 10 during image guided
surgery. At 50, the medical instrument 10 is tracked using
conventional image guided surgery tracking methods. For example,
the medical instrument 10 may be tracked through an
electromagnetic, optical, or inertial position tracking system. The
conventional tracking system accurately tracks a general position
of the medical instrument 10. The conventional tracking system
accurately tracks the support member 12 and the proximal end 15 of
the medical instrument 14.
At the same time that the medical instrument 10 is tracked by the
conventional tracking system, the medical instrument is tracked by
the deflection tracking system, including strain gauges at 52. The
deflection tracking system tracks the deflection of the flexible
engaging member 14 of the medical instrument as described
above.
At 54, a control system, such as a microprocessor, processes and
combines data received from the conventional tracking system and
the deflection tracking system. Then, at 56, the processor displays
the combined data on a monitor to show the position of the medical
instrument 10, including the proximal and distal ends 15, 17 of the
flexible engaging member 14.
Embodiments of the present invention provide a system and method in
which a medical instrument may be tracked by a conventional
tracking system using methods known in the art. The tracking system
provides information regarding the general position of the medical
instrument. The use of the strain gauges on the medical instrument
provides a deflection tracking system that provides more specific
information regarding the location of the tip (i.e., the flexible
engaging member 14) of the medical instrument 10. Using information
provided by a conventional tracking system and information provided
by the deflection tracking system provides accurate information
regarding the location of the medical instrument.
While the invention has been described with reference to certain
embodiments, it will be understood by those skilled in the art that
various changes may be made and equivalents may be substituted
without departing from the scope of the invention. In addition,
many modifications may be made to adapt a particular situation or
material to the teachings of the invention without departing from
its scope. Therefore, it is intended that the invention not be
limited to the particular embodiment disclosed, but that the
invention will include all embodiments falling within the scope of
the appended claims.
* * * * *
References